In a groundbreaking study at the intersection of cultural heritage conservation and structural engineering, a team of researchers conducted an in-depth analysis of the crack propagation risks in classical garden rockeries, focusing on the He Garden in Yangzhou, China. Utilizing cutting-edge ground-based 3D laser scanning technology, the team meticulously captured the morphological and structural conditions of these ancient rockeries over a period spanning several years, revealing unprecedented details about their current state of preservation and underlying damage mechanisms. This investigation provides valuable insights into both the physical deterioration processes and the broader challenges of maintaining historically significant landscapes in the face of natural and anthropogenic stressors.
The research hinged on data collected through two distinct point-cloud scans performed using a Trimble RealWorks 3D laser scanner. The initial scan was conducted in September 2021, followed by a subsequent scan in January 2025. These scans afforded a comprehensive three-dimensional representation of the Small-rock Mountain Adobe rockery within He Garden, allowing for precise detection and mapping of crack patterns and other structural anomalies. Such high-resolution temporal snapshots are critical in assessing degradation trends and validating the risk assessments derived from fracture mechanics principles.
Visual surveys complemented the laser scanning data, enabling the team to identify and classify real-world damage manifestations on the rockeries’ surfaces. The exhaustive visual damage survey uncovered a total of 14 significant structural cracks within the Small-rock Mountain Adobe rockery. Notably, two of these cracks were attributed mostly to settlement of the foundational supports, primarily localized near the revetment zones – areas where structural reinforcement meets natural earth or built embankments. This settlement-induced cracking signals ongoing shifts that may jeopardize the integrity of the rockery if left unaddressed.
Beyond settlement concerns, the majority of the observed cracks—twelve in number—were attributed to stress-induced fissures. These cracks reflect the stresses generated within the rockery’s composite materials, driven by environmental fluctuations such as thermal expansion, moisture variation, and perhaps internal load redistributions. Such fissures tend to propagate progressively, making them pivotal indicators of emerging structural vulnerabilities within heritage garden components.
Adhesive detachment was identified as the cause behind two of the cracks, denoting failures at the bonding interfaces between different rock elements or between rock and mortar components. These detachments signal weakening cohesion within the rockery fabric and point to potential aging or degradation of the materials that bind these stones in place. Furthermore, one crack was linked to plant-root intrusion—a phenomenon where woody roots penetrate and grow within structural joints, physically exerting forces that cause splitting and fracturing of rock elements, compounding the deterioration process.
Interestingly, the research team found that several cracks resulted from the interplay of multiple structural damage mechanisms rather than singular causes. This multifactorial genesis highlights the complex stress environment within historic rockeries, where biological, mechanical, and geotechnical factors interplay dynamically over time. Understanding these intertwined mechanisms is crucial for developing accurate predictive models and effective conservation strategies.
The study further enriched its analytical framework by employing a zoning diagram specific to the Small-rock Mountain Adobe rockery, dividing the structure into distinct sectors such as the West side cavern, Main peak east to central area, Central cavern entrance, and others. This spatial categorization afforded fine-grained scrutiny, enabling the correlation of observed damage to particular structural or environmental conditions characteristic of each zone. For instance, cracks near revetment areas were clearly linked to foundation settlement phenomena, whereas fissures scattered throughout the main peaks suggested stress concentrators inherent to those zones.
Building on a classification system originally posited by Fu et al., the researchers refined the categorization of crack-related damage causes, embedding it in a local context and validating it against newly collected empirical evidence. This methodical classification charted damage under categories such as settlement-induced cracking, stress fissures, adhesive detachment, and biological intrusion, giving the conservation community a robust terminology and detection guide grounded in both classical theories and modern observation technologies.
Extending beyond a single rockery, the investigation encompassed four separate rockeries within the He Garden cultural heritage site, synthesizing crack damage data to establish a comparative baseline of structural integrity across the site. These comparative results revealed how differing rockery designs, materials, and exposure conditions manifest unique structural challenges. One noteworthy outcome was that the Pond-Centered Pavilion Hushi rockery exhibited no visible structural cracks upon on-site inspection, thus highlighting variability in preservation states and possibly differing maintenance histories or environmental exposures.
The analytical methodology leveraged fracture mechanics principles, particularly Linear Elastic Fracture Mechanics (LEFM), to interpret crack propagation risks quantitatively. LEFM elucidates how existing cracks may evolve under operational stresses, offering predictive insights that can inform intervention thresholds before irreversible damage ensues. By adopting this theoretical scaffolding, the study transcended descriptive assessment to engage proactively with risk management trajectories for these priceless garden artifacts.
The adoption of advanced laser scanning technology, coupled with rigorous visual inspection and fracture mechanics analysis, exemplifies a transformative paradigm in heritage science. This integrative approach ensures that cultural relics subjected to multidimensional stresses are safeguarded through evidence-driven monitoring and maintenance. In the context of the Yangzhou He Garden, such innovation not only preserves physical structures but also the intangible heritage and aesthetic values they embody, fostering heritage resilience amid environmental and anthropogenic change.
Moreover, the findings pointed to the necessity of targeted conservation measures addressing the causative factors behind crack formation. For foundation settlement issues, soil stabilization or underpinning techniques could be explored. For stress-induced fissures, material reinforcement strategies or environmental controls may reduce cyclical stress effects. Meanwhile, biological damage from roots suggests the need for ongoing vegetation management within proximity to vulnerable rock elements.
The successful application of repeat 3D scans over a multi-year timeline opens avenues for longitudinal studies correlating climatic variation, visitor impact, and material aging to structural health. Future research might harness this dynamic monitoring framework to establish predictive maintenance schedules, ensuring timely intervention before minor cracks evolve into detrimental fractures.
In sum, this comprehensive study on the He Garden rockeries intertwines state-of-the-art laser scanning technology, thorough visual inspections, and fracture mechanics theory to not only diagnose existing damage but also forecast and mitigate future risks. It stands as a template for sustainable preservation practices applicable to similar heritage sites globally, balancing cultural reverence with scientific rigor in the stewardship of historical landscapes.
Subject of Research:
Crack propagation risk in classical garden rockeries through advanced 3D laser scanning and fracture mechanics analysis.
Article Title:
Crack propagation risk threshold of classical garden rockeries based on LEFM.
Article References:
He, Z., Zhang, X., Fu, L. et al. Crack propagation risk threshold of classical garden rockeries based on LEFM. npj Herit. Sci. 13, 535 (2025). https://doi.org/10.1038/s40494-025-02061-7
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